"Right now we're shutting the system down," club spokesman Jay Alves announced outside Coors Field, drawing boos from fans. "We expect to be online at some point."
"We're as frustrated and disappointed as they are," Alves said.
Alves had said last week that the Rockies were prepared for any computer problems.
On Monday, there were 8.5 million attempts to connect with the computers in the first 90 minutes after sales started, he said, and only several hundred tickets had been sold before the system had to be shut down.
The Rockies put as many as 60,000 tickets up for sale online only, and team officials said their computers were ready to handle the expected crush. But two hours after tickets went on sale, many fans reported they could not get access to the ticket-sales Web site.
Officials with the Rockies and Major League Baseball did not immediately return calls.
Irvine, Calif.-based Paciolan Inc., which is running the computers for the Rockies' World Series ticket sales, said the crash affected the company's entire North American system.
Paciolan CEO Dave Butler said he did not yet know whether demand for Rockies tickets caused the crash, reports CBS News affiliate KCNC.
"This is not the Rockies' fault in anyway whatsoever," Butler said. "We are working hard to address it."
About 20 people lined up in near-freezing temperatures outside the Denver Public Library before it opened in hopes of using public-access computers to score tickets.
"If you can't get tickets here, you're going to have to pay $200, $300 above face value," said Clayton McLeod, a 26-year-old heavy-machine operator who took the day off to try to get seats.
McLeod said he has Internet access from his apartment building but thought the library's computers might be faster. His mother, father, uncle and girlfriend were trying to buy tickets from other computers, he said.
His boss, also a Rockies fan, agreed to give him the day off and asked McLeod to get tickets for him, too.
"We'll see how many I'll get," McLeod said.
The Rockies limited sales to four per person per game.
The Series opens in Boston with games on Wednesday and Thursday. Games 3 and 4 will be on Saturday and Sunday in Denver. If there is a Game 5, it will be played Monday in Denver.
Coors Field seats more than 50,000, but about 30,000 spots per game are allotted to season-ticket holders, the two teams and Major League Baseball.
Season-ticket holders got a chance to buy their tickets last weekend. Prices range from $65 to $250.
Tickets originally were to be sold at Coors Field and Rockies' Dugout Stores in the Denver area, as well as online. The team announced Wednesday all sales would be online, saying that would be more fair.